Method and apparatus for increasing a probability that a dual-band mobile station will acquire a desired autonomous system

ABSTRACT

A method for operating a dual-band mobile station ( 10 ) includes a first step of (a) storing information in the mobile station. The stored information includes an ordered list of frequency bands (Band Order Table  24 A). For example, at least one frequency band is an 800 MHz frequency band and at least one other frequency band is a 1900 MHz frequency band. The stored information further includes an identity ( 24 B) of a band wherein an acceptable control channel was last located. A next step (b) is executed in response to a user invoking a search procedure to locate a new non-public system. This step accesses the memory to determine the identity of the band wherein an acceptable control channel was last located, and marks this band as a band to be searched. A next step (c) collects signal strength measurements on channels in the band to be searched and executes a channel search procedure to locate a control channel of a desired non-public system within the band to be searched. If a desired non-public system is not located in the band to be searched, a next step (d) accesses the memory to obtain a next band to be searched from the Band Order Table. The method repeats steps (c) and (d) until either the ordered list of frequency bands is exhausted or a desired non-public system is located, thereby enabling a non-public system to be located in a band other than the current band of the mobile station.

FIELD OF THE INVENTION

[0001] This invention relates generally to radiotelephones and, in particular, to radiotelephones or mobile stations such as those capable of operation with a public system and with an autonomous system, such as a Private or Residential network.

BACKGROUND OF THE INVENTION

[0002] In modern mobile telecommunications systems a mobile station may have a choice as to whether to operate with a public cellular system or with an autonomous system, such as a Residential system or a Private system. Typically it will be desirable to operate with a selected autonomous system, which may provide a more favorable rate structure than the public cellular system(s), or that may provide a desired service not offered by the public cellular system(s). A particular autonomous system may be a Residential system that serves the user's home, or a Private system that serves the user's workplace.

[0003] One such modern cellular system is referred to as IS-136, which is described in IS-136.1, Rev. A, February 1996, and subsequent updated releases. This system employs Digital Control Channels (DCCHs) that enable a mobile station to gain access to the system. When a mobile station scans for and subsequently monitors a DCCH, it is said to be “camped” on that particular DCCH. Page messages and other information are received from the DCCH.

[0004] In Section 6.3.19 of IS-136.1 there is described a non-public mode search procedure that is to be implemented by IS-136 compliant mobile stations. As defined, while camping on a DCCH a mobile station user may decide to initiate a Non-Public Mode Search Condition in order to search for service with an alternate system (System Identification (SID), Private System Identification (PSID), or Residential System Identification (RSID)) on the current DCCH and/or other DCCHs. Two possible procedures are defined for Non-Public Mode Search: New PSID/RSID Search and Manual System Search.

[0005] Discussing first the New PSID/RSID Search procedure, when the user invokes this procedure the mobile station proceeds as follows. First the mobile station collects one signal strength measurement on each frequency in the current frequency band. The band can be one of the following: 800 MHz A or B, or 1900 MHz A, B, C, D, E, or F. Next, the mobile station makes a list of up to 24 channels with the strongest signals, and then tunes to the strongest channel in the list. The mobile station then determines if this channel contains a DCCH. If the channel contains a DCCH, the mobile station reads the Fast Broadcast Control Channel (F-BCCH) and determines therefrom if the DCCH is marked with a non-public Network Type (Private and/or Residential) that is enabled in the mobile station. If this is the case, the mobile station marks the DCCH as DCCH_(—)1. If the channel does not contain a DCCH, or if the DCCH is not marked with a non-public Network Type that is enabled in the mobile station, then a determination is made if this is the last channel in the channel list. If it is, the procedure ends, otherwise the mobile station reads the next strongest channel in the channel list and the process repeats.

[0006] After possibly performing a Test Registration procedure, and marking an appropriate PSID/RSID as SYS_(—)1, the mobile station displays an indication of SYS_(—)1 to the user. If the user selects SYS_(—)1, and after other processing, a determination is made if DCCH_(—)1 is the current DCCH. If it is not, the mobile station adds DCCH_(—)1 to a list of channels identified as requiring measurements (see Section 6.3.3.1, Control Channel Locking). The mobile station then, after an appropriate delay required for channel measurement purposes (see Section 6.3.3.3), declares a Priority System Condition (see Section 6.2.3) using DCCH_(—)1 as the only reselection candidate. The CELLTYPE for DCCH_(—)1 defaults to PREFERRED until otherwise determined. In addition, the mobile station determines the MS_ACC_PWR, RSS_ACC_MIN, SS_SUFF and DELAY (see Section 6.3.3.4.2) for DCCH_(—)1 prior to involving or while executing the Control Channel Reselection procedure (see Section 6.3.3).

[0007] In the Manual System Search procedure, the mobile station proceeds as follows. The mobile station first searches the current DCCH and neighboring DCCHs (including Private Operating Frequencies (POFs) if they exist) for all candidates that support one or more of the PSIDs, RSIDs, and preferred SID that the mobile station subscribes to. The mobile station then displays a PSID/RSID Alphanumeric Name of each PSID or RSID supported by the candidate control channels that match a PSID or RSID stored in the mobile station, and the Alphanumeric System ID of the preferred SID. The mobile station then marks as DCCH_(—)1 the candidate control channel supporting the SID, PSID, or RSID matching the Alphanumeric System ID or PSID/RSID Alphanumeric Name selected by the user. If more than one candidate control channel supports the selected PSID, RSID, or SID, then the candidate with the highest signal strength is marked as DCCH_(—)1. If no SID, PSID, or RSID is selected by the user, the procedure is simply terminated.

[0008] If DCCH_(—)1 is not the current DCCH, then the mobile station performs the same steps as described above for the New PSID/RSID search procedure, i.e., adding DCCH_(—)1 to the list of channels identified as requiring measurements, etc.

[0009] As was discussed above, when executing the New PSID/RSID Search procedure the mobile station collects one signal strength measurement on each frequency in the current frequency band. The current band can be one of the following: 800 MHz A or B, or 1900 MHz A, B, C, D, E, or F. Reference in this regard can be had to FIGS. 4 and 5, which illustrate the channel numbers and frequency bands specified for 800 MHz and 1900 MHz operation, respectively, in IS-136.2, Sections 2.1.1.1.1 and 2.1.1.1.2, respectively.

[0010] However, a problem is created by this search procedure as currently specified, in that a desired Private or Residential system may be located in a different band than the mobile station's current band. If only the mobile station's current band is searched then the desired Private or Residential system will most likely not be located and acquired.

OBJECTS AND ADVANTAGES OF THE INVENTION

[0011] It is thus a first object and advantage of this invention to provide an improved method for executing a system search procedure with a mobile station.

[0012] It is a further object and advantage of this invention to provide a method, and a mobile station constructed to operate in accordance with the method, for increasing a probability that a mobile station will acquire and register with a desired non-public or autonomous system.

SUMMARY OF THE INVENTION

[0013] The foregoing and other problems are overcome and the objects of the invention are realized by methods and apparatus in accordance with embodiments of this invention.

[0014] A method of this invention is disclosed for operating a mobile station, the method including a first step (a) of storing information in the mobile station. The stored information includes an ordered list of frequency bands, where each frequency band includes at least one channel. For example, at least one frequency band is an 800 MHz frequency band and at least one other frequency band is a 1900 MHz frequency band. The stored information further includes an identity of a band wherein an acceptable control channel was last located. In the preferred embodiment of this invention the control channel is a digital control channel (DCCH).

[0015] A next step (b) is executed in response to a user invoking a search procedure to locate a new non-public system. The non-public system may be one of a Residential system or a Private system. This step accesses the memory to determine the identity of the band wherein an acceptable control channel was last located, and marks the band wherein the acceptable control channel was last located as a band to be searched.

[0016] A next step (c) collects signal strength measurements on channels in the band to be searched and executes a channel search procedure to locate a control channel of a desired non-public system within the band to be searched.

[0017] If a desired non-public system is not located in the band to be searched, a next step (d) accesses the memory to obtain a next band to be searched from the ordered list of frequency bands and marks the next band as the band to be searched.

[0018] The method repeats steps (c) and (d) until either the ordered list of frequency bands is exhausted or a desired non-public system is located, thereby enabling a non-public system to be located in a band other than the current band of the mobile station.

[0019] If the step of accessing the memory to determine the identity of the band wherein an acceptable control channel was last located is not successful, the method instead includes a step of accessing the memory to obtain a predetermined band (for example the first band) to be searched from the ordered list of frequency bands and then marking the predetermined band as the band to be searched.

BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The above set forth and other features of the invention are made more apparent in the ensuing Detailed Description of the Invention when read in conjunction with the attached Drawings, wherein:

[0021]FIG. 1 is a block diagram of a mobile station that is constructed and operated in accordance with this invention;

[0022]FIG. 2 is an elevational view of the mobile station shown in FIG. 1, and which further illustrates a plurality of cellular communication systems to which the mobile station can be bidirectionally coupled through wireless RF links;

[0023]FIG. 3 is a logic flow diagram illustrating a presently preferred method for performing a multi-band search procedure with the mobile station illustrated in FIGS. 1 and 2; and an associated PSID.

[0024] The mobile station 10 of FIG. 1 includes a transceiver comprised of a modulator (MOD) 14A, a tuneable transmitter 14, a tuneable receiver 16, a demodulator (DEMOD) 16A, and a controller 18 that provides signals to and receives signals from the transceiver. These signals include signalling information in accordance with the air interface standard of the applicable cellular system, and also user speech and/or user generated data. As was indicated above, the transmitter, receiver, modulator and demodulator may be at least dual-mode capable, and may operate with the frequencies, modulation type, access type, etc. of several of the various public and autonomous systems in the environment of the mobile station 10.

[0025] It is understood that the controller 18 also includes the circuitry required for implementing the audio and logic functions of the mobile station. By example, the controller 18 may be comprised of a digital signal processor device, a microprocessor device, and various analog to digital converters, digital to analog converters, and other support circuits. The control and signal processing functions of the mobile station are allocated between these devices according to their respective capabilities.

[0026] A user interface includes a conventional earphone or speaker 17, a conventional microphone 19, a display 20, and a user input device, typically a keypad 22, all of which are coupled to the controller 18. The keypad 22 includes the conventional numeric (0-9) and related keys (#,*) 22 a, and other keys 22 b used for operating the mobile station 10. These other keys 22 b may include, by example, a SEND key, various menu scrolling and soft keys, and a PWR key. The mobile station 10 also includes a battery 26 for powering the various circuits that are required to operate the mobile station 10.

[0027] The mobile station 10 also includes various memories, shown collectively as the memory 24, wherein are stored a plurality of constants and variables that are used by the controller 18 during the operation of the mobile station. For example, the memory 24 stores the values of various cellular system parameters and the number assignment module (NAM). An operating program for controlling the operation of controller 18 is also stored in the memory 24 (typically in a ROM device). The memory 24 may also store data, including user messages, that is received from the BMI 32 prior to the display of the messages to the user.

[0028] The memory 24 also stores, in accordance with an aspect of this invention, a Band Order Table 24A. The Band Order Table 24A has a plurality of entries constituting a list a frequency bands (see FIGS. 4 and 5) and is ordered in the way the frequency bands are to be searched. The Band Order Table 24A can contain from one band to all bands (e.g., 800 MHz A and/or B, 1900 MHz A, B, C, D, E, and/or F). The memory 24 also stores Last-Used DCCH Information (channel/frequency band) 24B which is updated when the mobile station 10 camps on an acceptable or useable DCCH. The Band Order Table 24A and Last-Used DCCH Information 24B are preferably stored in a permanent (non-volatile) portion of the memory 24. The memory 24 also typically stores a list of channels to be measured, one or more SIDs, RSIDs, PSIDs, as described above, as well as other relevant parameters, such as a current SCANINTERVAL value and DELAY value, as received from a Control Channel Selection Parameters message.

[0029] The operating program stored in the memory 24 may include routines to present messages and message-related functions to the user on the display 20, typically as various menu items. These include a capability to enable the user to invoke a New PSID/RSID search procedure, as described above with respect to the discussion of Section 6.3.19 of IS136.1 for the Non-Public Mode Search (NPS-DCCH) procedure. The memory 24 thus also includes routines for implementing the presently preferred search method described below in relation to FIG. 3.

[0030] Referring to FIG. 3, the above described New PSID/RSID Search and Manual System Search procedures are modified as follows.

[0031] When the user invokes the New PSID/RSID search procedure the mobile station 10 proceeds as follows. At Step 1 a the controller 18 accesses the memory 24 and obtains the last-used DCCH information. The associated last-used frequency band is marked as Band_(—)1. If the last-used DCCH information is not found in the memory 24, then the first frequency band found in the Band Order Table 24A is retrieved and marked as Band_(—)1.

[0032] At Step 1 b the mobile station 10 collects one signal strength measurement on each frequency in Band_(—)1.

[0033] The following steps 2 through 10 may then be executed as currently specified in IS-136.1.

[0034] More particularly, at Step 2 the mobile station 10 makes a list of up to 24 channels having the strongest signals, and at Step 3 tunes the receiver 16 and the transmitter 14 to the strongest channel in the list. At Step 4 the mobile station 10 determines if this channel contains a DCCH. If it does, the mobile station 10 reads the Fast Associated Control Channel (FACCH) and determines if the DCCH is marked with a non-Public Network Type (Private and/or Residential) that is enabled in the mobile station. If this is the case, the DCCH is marked as DCCH _(—)1. If the channel does not contain a DCCH, or if the DCCH is not marked with a non-Public Network Type that is enabled in the mobile station 10, control passes to Step 10 (described below).

[0035] At Step 5 a determination is made if a Test Registration is allowed on DCCH_(—)1, according to the non-Public Registration Control information element. If Test Registrations are allowed, then the mobile station 10 formulates a Test Registration message for all PSIDs/RSIDs supported on DCCH_(—)1, and then waits for a Test Registration Response on DCCH_(—)1. If Test Registrations are not allowed, then control passes instead to Step 10.

[0036] At Step 6, upon receiving the Test Registration Response from DCCH_(—)1, the mobile station 10 generates a list of PSIDs/RSIDs for which an “accepted” indication is provided, and marks an appropriate PSID/RSID in the “accepted” list as SYS_(—)1. If an accepted indication is not indicated for any of the PSIDs/RSIDs supported on DCCH_(—)1, control passes to Step 10.

[0037] At Step 7 the mobile station 10 displays the PSID/RSID Alphanumeric Name of the SYS_(—)1 non-Public System. The user then has the option to accept or reject the displayed non-Public System.

[0038] If the user selects SYS_(—)1, at Step 8 then the following sub-steps are executed.

[0039]8 a: If SYS_(—)1 is a PSID or RSID that is already stored in the mobile station 10, then update the stored PSID/RSID Alphanumeric Name.

[0040]8 b: If SYS_(—)1 is not a PSID or RSID that is already stored in the mobile station 10, then store the PSID or RSID and the PSID/RSID Alphanumeric Name along with the associated this invention, to Step lob. If the current channel is not the last channel in the channel list, then the mobile station 10 tunes to the next strongest channel in the channel list and control transfers back to Step 4.

[0041] Further in accordance with this invention, at Step 10 b the mobile station 10 again accesses the Band Order Table 24A in the memory 24 and obtains the next frequency band in the Band Order Table 24A. If all bands have been searched (i.e., the Band Order Table 24A is exhausted), then the search procedure terminates. If all of the bands have not yet been searched, then the mobile station 10 obtains the next frequency band in the Band Order Table 24A, marks the next frequency band as Band_(—)1 (i.e., the band to be searched), and control then transfers back to Step 1 b to collect one signal strength measurement from each frequency in Band_(—)1, and to then continue with Steps 2-10.

[0042] As an example, assume that the Band Order Table 24A contains bands A, B, C, D, E, and the Last Used DCCH 24B is in band B. In this case, the first band searched will be band B. If unsuccessful, then the next band to be searched will be band A, followed by band C if the search of band A is unsuccessful. That is, the bands are preferably stored in the Band Order Table 24A in order of priority, with the most significant or desirable band being listed first, followed by the next most desirable band, etc. However, the use of other band search orders are within the scope of the teaching of this invention.

[0043] It can be seen that the use of the teaching of this invention increases the probability that a user will be able to locate a desired non-public system when performing a New PSID/RSID Search procedure, as all frequency bands specified in the Band Order Table 24A (including one or more 1900 MHz bands) can be methodically searched.

[0044] The Band Order Table 24A can contain all possible frequency bands that the mobile station 10 is capable of operating with, or only a selected sub-set of these bands. The Band Order Table 24A can be stored permanently in ROM, or in a writable non-volatile memory such as EAROM or a battery-backed static RAM. In this latter case the mobile station 10 may be programmed so as to give the user (using the user interface or a connection to computer), a dealer, or a system operator an ability to alter the contents of the Band Order Table 24A. By example, a suitable signalling protocol can be defined for the air interface to enable a system operator, or some other entity located at a remote location, to remotely program the contents of the Band Order Table 24A to add or delete frequency bands, as well as to change the order of the frequency bands in the Band Order Table, thereby resulting in the bands being searched in a different order by the mobile station 10.

[0045] Although described above in the context of a specific air interface and specific frequency bands, it should be recognized that the teachings of this invention are not limited to only these presently preferred embodiments and further that a number of modifications to these teachings may occur to one skilled in the art. By example, the teaching of this invention is not limited for use only with systems constructed and operated in accordance with IS-136, or only with digital TDMA cellular systems, as CDMA and other wireless system types may benefit from the use of the teachings of this invention.

[0046] Thus, while the invention has been particularly shown and described with respect to preferred embodiments thereof, it will be understood by those skilled in the art that changes in form and details may be made therein without departing from the scope and spirit of the invention. 

What is claimed is:
 1. A method for operating a mobile station, comprising steps of: (a) storing information in a memory of the mobile station, the stored information comprising an ordered list of frequency bands, each frequency band comprising at least one channel, the stored information further comprising an identity of a band wherein an acceptable control channel was last located; (b) in response to a user invoking a search procedure to locate a new non-public system, accessing the memory to determine the identity of the band wherein an acceptable control channel was last located, and marking the band wherein the acceptable control channel was last located as a band to be searched; (c) collecting signal strength measurements on channels in the band to be searched and executing a channel search procedure to locate a control channel of a desired non-public system within the band to be searched; (d) if a desired non-public system is not located in the band to be searched, accessing the memory to obtain a next band to be searched from the ordered list of frequency bands and marking the next band as the band to be searched; and repeating steps (c) and (d) until either the ordered list of frequency bands is exhausted or a desired non-public system is located.
 2. A method as in claim 1 , wherein the desired non-public system is one of a Residential system or a Private system.
 3. A method as in claim 1 , wherein the control channel is a digital control channel (DCCH).
 4. A method as in claim 1 , wherein at least one frequency band is an 800 MHz frequency band, and wherein at least one other frequency band is a 1900 MHz frequency band.
 5. A method as in claim 1 , wherein if the step of accessing the memory to determine the identity of the band wherein an acceptable control channel was last located is not successful, the method instead includes a step of accessing the memory to obtain a predetermined band to be searched from the ordered list of frequency bands and marking the predetermined band as the band to be searched.
 6. A method as in claim 5 , wherein the predetermined band is the first band in the ordered list of frequency bands.
 7. A method as in claim 1 , wherein the step of storing information is accomplished in cooperation with a user interface of the mobile station.
 8. A method as in claim 1 , wherein the step of storing information is accomplished by receiving the information over the air from a remote location.
 9. A mobile station, comprising: a RF transceiver for bidirectionally communicating with base stations of public or autonomous communications systems; a user interface for displaying information to a user and for receiving an input from a user; a memory for storing information, the stored information comprising an ordered list of frequency bands, each frequency band comprising at least one channel, the stored information further comprising an identity of a band wherein an acceptable control channel was last located; and a controller coupled to said transceiver, to said user interface, and to said memory, said controller being responsive to a user invoking a search procedure to locate a new non-public system for accessing said memory to determine the identity of the band wherein an acceptable control channel was last located, and for marking the band wherein the acceptable control channel was last located as a band to be searched, said controller tuning said transceiver for collecting signal strength measurements on channels in the band to be searched and executing a channel search procedure to locate a control channel of a desired non-public system within the band to be searched, said controller being responsive to a condition that a desired non-public system is not located in the band to be searched, for accessing said memory to obtain a next band to be searched from said ordered list of frequency bands and for marking the next band in said ordered list as the band to be searched, said controller continuing to collect signal strength measurements and executing the search procedure until either the ordered list of frequency bands is exhausted or a desired non-public system is located.
 10. A mobile station as in claim 9 , wherein the desired non-public system is one of a Residential system or a Private system.
 11. A mobile station as in claim 9 , wherein the control channel is a digital control channel (DCCH).
 12. A mobile station as in claim 9 , wherein at least one frequency band is an 800 MHz frequency band, and wherein at least one other frequency band is a 1900 MHz frequency band.
 13. A mobile station as in claim 9 , wherein said controller is responsive to a condition wherein accessing said memory to determine the identity of the band wherein an acceptable control channel was last located is not successful, for instead accessing said memory to obtain a predetermined band to be searched from the ordered list of frequency bands and for marking the predetermined band as the band to be searched.
 14. A mobile station as in claim 13 , wherein said predetermined band is the first band in the ordered list of frequency bands.
 15. A mobile station as in claim 9 , wherein at least a portion of said ordered list of frequency bands is stored in said memory in cooperation with said user interface.
 16. A mobile station as in claim 9 , wherein at least a portion of said ordered list of frequency bands is stored in said memory by receiving information over the air from a remote location.
 17. A method for operating a mobile station, comprising steps of: (a) storing information in a memory of the mobile station, the stored information comprising a list having one or more entries, each entry corresponding to a frequency band comprising at least one channel, the stored information further comprising an identity of a frequency band wherein an acceptable digital control channel (DCCH) was last located; (b) in response to a search procedure being invoked to locate a desired one of a Residential system or a Private system, accessing the memory to determine the identity of the frequency band wherein the acceptable DCCH was last located, and marking the band as a band to be searched, else if the identity of the band wherein the acceptable DCCH was last located is not available, then selecting a predetermined entry in the list of frequency bands and marking the corresponding frequency band as the band to be searched; (c) collecting signal strength measurements on channels in the band to be searched and executing a channel search procedure to locate a control channel of a desired Residential system or Private system within the band to be searched; (d) if a desired Residential system or Private system is not located in the band to be searched, accessing the memory to obtain a next entry from the list of frequency bands and marking the corresponding band as the band to be searched; and repeating steps (c) and (d) until either the list of frequency bands is exhausted or the desired Residential system or Private system is located.
 18. A method as in claim 17 , wherein at least one frequency band is an 800 MHz frequency band, and wherein at least one other frequency band is a 1900 MHz frequency band.
 19. A method as in claim 17 , wherein the step of storing information includes a step of inputting information for at least one of adding an entry to the list, deleting an entry from the list, or re-ordering entries in the list.
 20. A method as in claim 19 , wherein the inputted information is received at least in part from one of a user interface of the mobile station or from a remote location. 